Absorption, attenuation, and grids Flashcards
(23 cards)
PEA results in complete
x-ray absorption
compton causes
scatter
attenuation
some penetrating x-rays are absorbed by tissues
exponential attentuation
absorption depends on tissues thickness
HVL measures x-ray
quality/penetrability
HVL
thickness of absorbing material needed to reduce x-ray intensity by half
types of filtering
- tungsten anode
- x-ray tube housing
- added filtration
exposing body parts with unequal thickness
compensatory filter
primary bean attenuated by 90%
tenth value layer (TVL)
scatter intensity depends on..
kVp, beam field size, and patients thickness
grid is a series of
lead strips –> cleans up scatter (up to 80%)
grid ratio
R=h/D
most frequent grid ratio used
8:1 to 10:1
higher ratio grids
less scatter but more radiation exposure is needed
paralleled grid flaw
grid cut-of artefact
grid cut-off
undesirable absorption of primary x-rays
grid cut-off is inversely related to
source image distance (SID)
disadvantages of moving grids
bulky mechanism and blurring effect
stationary grids mostly used for
portable radio and upright horizontal views
higher grid ratio can be met by
increase in mAs
mAs should be increased
10% for each cm of air-gap
commonly obtained using air-gap technique
lateral cervical
used with out grid to reduce scatter and maintain contrast
air-gap technique
